The invention concerns a compact-disk plaYer wherein, once a compact disk has been inserted, the table of contents of the disk is read out and at least some of it entered in a memory.
The article "Zusammenstellen eines CD-Programms" ["Compiling a CD program"], Funkschau 15, 7/18/1986, pages 26-28, describes the kinds of data that are basically stored on a compact disk and how the player processes them.
Every compact disk contains a table of contents, wherein data are stored that provide information as to the number of program blocks stored on the disk, their starting times, and the total playing time of the disk. The individual program blocks are generally pieces of music, although they can also be spoken texts or sound effects for adding sound to motion pictures or slide shows. Up to 99 program blocks can be stored on one compact disk, although there are usually no more than 10 to 20 different pieces on a musical disk.
The table of contents on a compact disk has the format illustrated in the figure. The first block, A0, contains the title of the first piece of music, the second block, A1, that of the last piece of music, and the third block, A2, the total playing time of the disk. The next blocks, D1 through Dn contain the starting times of the individual pieces of music recorded on the disk. Blocks A0, A1, A2, and D1 through Dn are collected into a group, in which the table of contents of the compact disk is stored once.
Since all of the storage space available for the table of contents on the disk is occupied by several of these directly adjacent groups, the data in the table is stored multiply redundant.
While the compact disk is being played, starting-time points D1 through Dn, which constitute the major portion of the data stored in the table of contents, are utilized to calculate the starting times of the individual pieces. Only the more expensive compact-disk players, however, have enough memory addresses to store the total table of contents, and the simpler players can store only some of it, the first 10 of n pieces of music for example. This means that the memory will contain only the first three blocks, A0 through A2, plus blocks D1 through D10, and there is no room for the remaining blocks, D11 through Dn.
To read out a block from the compact disk and store its data in the memory a player takes about 40 milliseconds. Thus, if 99 pieces of music are actually recorded on the disk, reading them out and storing the three blocks A0. A1, and A2 plus the 99 blocks D1 through D99 will take approximately (3 +99).times.40 msec=4.08 sec if the beam of light that scans the data happens by chance to be at the beginning of the first block A0 of a group at precisely the instant it begins reading. The probability of such a desirable event, however, is very low.
The example of a compact-disk player that can store the titles of ten pieces of music and of a compact disk that contains 50 pieces of music will now be utilized to illustrate how long the read-out and entry time can be in certain situations.
At the commencement of the read-out and entry process the beam of light may be on block D11, which contains the starting time of the 11th piece of music. The 40 blocks D11 through D50 will have to be scanned before read-out and entry of the blocks A0 through A2 and D1 through D10 in the next group can begin. Since it will take 40.times.40 msec=1.6 sec to read blocks D11 through D 50 and another 13.times.40 msec=0.52 sec to read out and enter blocks A0 through A2 and D1 through D10, it will take 1.6+0.52 sec to start playing the first piece of music.
The time that elapses before the first piece of music can be played, however, can be even longer when one block, block D10 for example, is illegible due to a scratch on the disk. In this situation the compact-disk player keeps on reading until it arrives at the block D10 in the next group, which should be legible. Thus, blocks D11 through D50, followed by the blocks A0 through A2 and D1 through D10 in the following groups are read. Since the player needs another 53.times.50 msec=2.12 sec to read these 40+3+10=53 blocks, the listener must wait approximately 4 sec before he can listen to the first piece of music.